Small sized stroboscopic tube for photographic use

ABSTRACT

A discharge tube provided with a pair of electrodes is filled with an inert gas and is adapted for use with photographic apparatus as a stroboscope or the like. At least one getter of metals such as titanium, tantalum and zirconium is mounted on or near one of the electrodes. The getter is heated by the near electrode and the ion flow in the tube.

United States Patent 91 (Ihow SMALL SIZED STROBOSCOPIC TUBE FOR PHOTOGRAPI-HC USE [76] Inventor: Siting Cheung Chow, 12A Suffolk Road, Kowloon, Hong Kong [2 2] Filed: June 21, 1971 Appl. No.: 155,144

[30] Foreign Application Priority Data June 24, 1970 Japan ..45/62297 [52] US. Cl. ..313/178, 313/180, 313/217,

315/241 5 [511 lint. cu. ..H01j 61/26 581 FieldoiSearch...; ..3-l3/178,l80,-l85,

[56] References Cited UNITED STATES PATENTS 3,543,076 11/1970 Haslund .;.....3l3/178X 3,168,668 2/1965 Rexer ....3l3/l84 51 Apr. 10, 1973 Primary Examiner- Palmer C. Demeo Attorney-Donald Gunn [57] ABSTRACT 'A discharge tube provided with a pair of electrodes is filled with an inert gas and is adapted for use with photographic apparatus as a stroboscope or the like.

At least one getter of metals such as titanium, tantalum and zirconium is mounted on or near one of the electrodes. The getter is heated by the near electrode and the ion flow in the tube.

7 Claims, 3 Drawing Figures PATENTEUAFR 1 01m 3; 727, 089

+ WWW J 3Mr 2 1 DC 260V 1000uF 12 u. 7

1* 9 ,--0.02uF 3 1O 1 Sking C, Chou) "J Donald Gull SMALL SIZED STROBOSCOPIC TUBE I I PHOTOGRAPHIC USE RELATED APPLICATION,

The present application is based upon the Applica-' tion for Utility Model Registration, Ser. No.'45-62297 filed by the same Applicant in Japan on June 24, 1970.

This invention relates to a discharge tube having stableoperating characteristics over a longjperiod of time, and yet which is small, and simple inconstruction and easy to manufacture. I

The flash discharge tube constructed according to the invention is especially useful in photographic apparatus .as a stroboscope and the likebecause it maintains stable luminous performance in spite of frequent I use over a long period of time.

Discharge tubes known in the prior art have certain deficiencies, for example, one drawback is that after frequent use, the tube fails to start unless'a voltage.- I higher than its design voltage is applied. The glass cj'onf tainer of the tube blackens on depositing gases and other impurities formed by the electric discharge, which lowers its luminousperformance and which can sometimes crack the bulb. When the discharge tube is used as a photographic flash, the loss of luminous perit has been necessary to heat it by supplying an electric current to it. This complicates the construction of the discharge tube to such an extent that it is very difficult,

if not impossible, to position a metal getter in small discharge tubes found most desirable in photographic applications.

It is, therefore, an object of this invention to provide a discharge tube in which the drawbacks of the tubes of the prior art are eliminated. According to this invention, an anode and a cathode are incorporated in a sealed glass tube and a metal getter of titanium, tantalum and zirconium is mounted on or near one end of the anode or the cathode. When the tube is in use, the heat generated by the collision of electrons or ions against the getter and the heat conducted from the connected electrode to the getter heats the getter to anoptirnum temperature at which the getter acts most effectively. Thus, the discharge tube according to this invention does not include heating devices for the getter.

A preferred embodiment of the discharge tube according to this invention will now be described withh formance caused by the blackening of the bulbmakes it difficult to use such a flash apparatus ora 'stroboscope successfully. I I

To avoid the mentioned above drawbacks,one'soludiscourages use of the discharge tube, for example, as a photographic apparatus or a stroboscope inview'of the fact that a rather smalltube is preferable. I I I For example, a small flashdischarge tube for use as a' photographic apparatus might have a glasstube which is4 mm in diameter and mm in length. The tube en.- closes an anode and a cathode, both in the form of. a thin tod which are disposed at opposite ends. The tube is filled with an inert gas such as helium, neon,argon,

stored on a condenser in an appropriateelectric circuit is momentarily discharged to flow. through bothflelectrodes of the tube. Though the discharge lasts only for a veryshort period of time, the tube liberates a large amount of energy and theheat so generated creates a quantity-of unwanted gases and other impurities. In a small tube, the unwanted gases and impurities are not readily disposed and tend to coat the glass tube, .often degrading the performance of the flash.

To correct the above problem, a getter is often used to absorb the undesirable products created by discharge. Barium has usually been used as a getter for a flash discharge tube. But barium readily vaporizes when heated, and adheres to the wall of the tube and reduces its transparency. When the wall becomes coated, the tendency to absorb heat increases and a hot spot may be formed in the tube so that the tube is liable to crack. The coated wall also lowers the luminous performance of the tube. Furthermore, after frequent use, the tube will require a voltage higher .thanthe design voltage to initiate discharge and as a consequence, the effective life of the bulb will be substantially shortened.

It is known that metals such as titanium, tantalum and zirconiumabsorb a large volume of certain gases I when they are heated to an elevated temperature. When one of these metals is used as a getter, however,

, tion is to make the bulb relatively large, This- 40 krypton, or xenon. The tube flashes when the charge reference, to the accompanying drawings, in which: I I

I 1 is a side elevation insection of a preferred embodiment of the discharge tube according to this invention; III J FIG. 2 is an enlarged side view showing one end of the cathode and a getter mounted thereon; and

. FICLB shows a circuit for operating the discharge tube according to this invention.

j Referring now-to FIG. 1,the numeral 1 denotes a glass tube-,measuring for example, 3.6 mm in outer diameter by 40' mm in length An anode 2 and a cathode-3 are made of thin tungsten rod, and are incorporated into the'tube'l'ina sealed manner. The tube 1 is filled with an inert gas such as helium, neon, argon, krypton or xenon under optimum pressure. Asmall piece of titanium S is fixed by spot welding or otherwise directly on or near one. end 4 of the cathode 3, The

titanium piece5 maypre ferably be disposed-in such a manner that it projects tosome extent-beyond the end 4 of the cathode 3ftoward the anode 2 as shown in FIG.

' 1. The cathode 3 is covered-all over its surface with a thin film ofbarium-oxide to ensure a better emission of means in an atmosphere .of oxygen and nitrogen and,

the nitrogen gas' is exhausted. through an outlet (not shown). The barium remaining inthe tube combines withthe residual oxygen to, form a thin film of barium oxide on the surface of the rod 3. Then, a' selected inert gas is introduced into the tube, and the tube sealed, by known methods. The numeral 7 indicates a starting electrode, and the outer surface of the glass tube is covered witha transparent conductive film, e. g., a thin tin oxide NESA coating, toens ureeasier'passage of an electric current through the wall of the tube.

It is not always necessary to disposethe titanium piece 5 projecting from the end 4 of the cathode, but

the getter may be located slightly, say about 3 mm, behind the end 4. An important factor in this connection is the use of a getter of metal, e.g., titanium in a position where the getter is heated by the electrode which supports it and, additionally by the emission electrons or ions produced by discharge between electrodes. The getter preferably has the form of a U- shaped ribbon 5 mounted on the end 4 of the cathode 3 as shown in FIG. 2. It will, however, be observed that the getter assumes some other shape, and is disposed as any other position on the cathode, depending on the application and characteristics required of a particular discharge tube, without departing from the scope and spirit of this invention.

In operation, electrons move from the cathode 3 to the anode 2. Positive ions are created by the emission and collide against the titanium piece 5 and the cathode 3, so that the getter 5 is heated by-the ions colliding thereagainst. The getter 5 is also heated by thermal conduction from the end of the cathode 3 which is raised to a higher temperature. Thus, it will be noted that the getter 5 is heated to an optimum temperature for absorbing unwanted gases produced by the intensive but brief electric discharge. Therefore, the harmful gases produced by discharge are absorbed by the titanium piece or getter 5, and the atmosphere in the discharge tube is always kept sufficiently pure and in its proper condition.

Reference will now be made to FIG. 3 which shows an electric circuit for operation of this invention. The anode 2 and the cathode 3 are connected to a direct current power source. A relatively large condenser 9 is directly connected to these two electrodes, and a second condenser 10 is connected to them through a resistance 11. A primary coil 12 is provided to connect the terminals of the condenser 10 via a switch 13, and a secondary coil 14 is connected to the starting electrode 7 at one end thereof and is grounded at the other end. It has been found from experiments that when various electric components have, for example, values as shown in FIG. 3, the switch 13 may successfully be actuated to produce a flash discharge in the tube. Of course, other component values may be used.

The performance of the flash tube of the present invention is quite good. From experiments, in which five discharge tubes filled with xenon were used, it was found that all the tubes required a starting voltage of approximately 185 volts before substantial useage. Five thousand flash discharge tests were conducted with each of those five tubes using the electric circuit shown in FIG. 3. After this many tests, a slight drop in the starting voltage down to approximately 180 volts was observed on each of the tubes.

Reference has been made in the foregoing description of the preferred embodiment of this invention to a discharge tube wherein a titanium piece or getter 5 is disposed on or near the end 4 of a cathode 3. It will, however, be noted that the getter 5 may alternatively be mounted on or near the corresponding end of an anode 2. In this case, the heat required to raise the temperature of the getter is provided by the collision of electrons or negative ions against the getter and by thermal conduction from the end of the anode. It will also be observed that a getter may be mounted on each of the anode and the cathode. Moreover, it will be understood that the rod shaped electrodes described in connection with a preferred embodiment of this invention may instead be in the form of a ball, a disc or any other shape depending on the type, application and characteristics required of a particular discharge tube. Likewise, such metals as zirconium and tantalum have proved themselves as getters.

Several advantages of the flash tube of this invention should be noted.

When the getter is mounted on or near one end of at least one of the electrodes, the getter is easily heated to an optimum temperature. Additionally, it is heated most effective by the heat generated by the collision of electrically charged particles against the getter. Consequently, the getter does not require any special means for heating it. Moreover, the getter can be attached to or near the electrode easily. The getter is small and the absence of a heater permits the use of a very small space for its incorporation in the tube. Therefore, the discharge tube fabricated according to this invention is reduced in size to an extent not possible with a discharge tubes of the prior art in which a solid getter is used.

The use of a getter of solid material such as titanium, tantalum and zirconium prevents or reduces the undesirable dimming or blackening of the tube wall and the abnormally high temperature gradients resulting from hot spots leading to cracking of the tube. This feature of the invention helps successfully reduce the diameter of the tube to a remarkable extent.

The getter is self activating and continues to be active throughout the duration of discharge in case of self-maintaining discharge, or becomes active upon occurrence of each discharge in case of flash discharge. Accordingly, the discharge tube according to this invention is ever ready to effect a proper discharge at any time.

The discharge tube according to this invention has a very long life because aging changes are eliminated or reduced. The starting voltage remains fairly constant even after repeated use over a long periodof time. Prior art discharge tubes of the kind herein discussed have often failed after repeated use because of an undesirable increase of the starting voltage and lowering of their luminous performance. Because of its features and advantages hereinabove described, however, the discharge tube according to this invention might even approach a life approximately ten times greater than that of any discharge tube available in the prior art.

While many changes may be incorporated in the embodiments herein desclosed, the scope of the present invention is determined by the claims.

What is claimed is:

1. In a small-sized closed stroboscopic tube in a straight transparent tube filled with inert gas, and adapted especially for photographic use, an improvement comprising:

a pair of oppositely disposed thin rod-shaped tungsten electrodes, said pair adapted to be connected as an 'anode and a cathode;

a solid getter material secured to or near one end of said electrodes, and adapted to be heated partially by the heat generated by discharge current flow in the tube wherein charged particles collide against said getter material, and partially by the heat conducted thereto from said cathode; and,

a thin film of barium oxide coating formed on said cathode. 2. The tube of claim 1 including similar getters on both of said electrodes.

' 3. The stroboscopic tube of claim 1 further including a thin transparent conductive film of NESA coating formed on that portion of the outer surface of said tube at one end of said tube.

4. The stroboscopic tube of claim 3 wherein said anode and cathode are connected to a direct current power source, and further including electric circuit means comprising: i

' a first condenser connected to said anode and cathode; a circuit including a second condenser and a resistance, and connected to said anode and.

cathode;

and a starting transformer disposed in such a manner that its primary coil is connected to the terminals of said second condenser, and that its secondary coil is connected to said thin NESA coating film at one end thereof, and grounded at the-other end.

5. The stroboscopic tube of claim 1 wherein said getter material is selected from the materials consisting of titanium, zirconium and tantalum.

6. The stroboscopic tube of claim 1 wherein said getter material is welded to said cathode and projects toward said anode.

7. The stroboscopic tube of claim I wherein said getter material is generally U-shaped, and is connected at both ends thereof with said electrode, the curved middle portion of said getter material projecting toward the other electrode. 

2. The tube of claim 1 including similar getters on both of said electrodes.
 3. The stroboscopic tube of claim 1 further including a thin transparent conductive film of NESA coating formed on that portion of the outer surface of said tube at one end of said tube.
 4. The stroboscopic tube of claim 3 wherein said anode and cathode are connected to a direct current power source, and further including electric circuit means comprising: a first condenser connected to said anode and cathode; a circuit including a second condenser and a resistance, and connected to said anode and cathode; and a starting transformer disposed in such a manner that its primary coil is connected to the terminals of said second condenser, and that its secondary coil is connected to said thin NESA coating film at one end thereof, and grounded at the other end.
 5. The stroboscopic tube of claim 1 wherein said getter material is selected from the materials consisting of titanium, zirconium and tantalum.
 6. The stroboscopic tube of claim 1 wherein said getter material is welded to said cathode and projects toward said anode.
 7. The stroboscopic tube of claim 1 wherein said getter material is generally U-shaped, and is connected at both ends thereof with said electrode, the curved middle portion of said getter material projecting toward the other electrode. 